Hematological malignancies are malignant neoplasms also termed “blood cancer”. Hematological malignancies may derive from either of the myeloid or the lymphoid cell line. The myeloid cell line normally produces granulocytes, erythrocytes, thrombocytes, macrophages and mast cells; the lymphoid cell line produces B, T, NK and plasma cells. Lymphomas, lymphocytic leukemias, and myeloma are from the lymphoid line, while acute and chronic myelogenous leukemia, myelodysplastic syndromes and myeloproliferative diseases are myeloid in origin.
Established treatments of hematological malignancy include administration of immunomodulatory imide drugs (IMiDs) to the subject. IMiDs are a defined group of compounds that comprises thalidomide and analogues of thalidomide (α-N-phthalimido-glutarimide), a glutamic acid derivative with anti-angiogenic, anti-proliferative, and immunomodulatory properties. Thalidomide analogues were initially synthesized with the aim of optimizing anti-angiogenic, anti-proliferative, and immunomodulatory properties while reducing toxicities. Several IMiD compounds, such as lenalidomide and pomalidomide, are currently the subject of extensive clinical evaluation in hematological malignancies. IMiDs have been successfully used in the treatment of multiple myeloma and other hemato-oncological diseases for some years.
In particular, treatment with IMiDs is among the established standard therapies for multiple myeloma and has led to a significant improvement in overall survival. Furthermore, IMiDs have been approved for the treatment of mantle cell lymphoma as well as the del(5q) variant of the myelodysplastic syndrome (MDS). A large number of clinical studies have demonstrated efficacy in the treatment of other hematologic malignancies such as chronic lymphocytic leukemia (CLL) or diffuse large B-cell lymphoma. In addition, there is increasing evidence for the efficacy of IMiDs on some non-hematologic neoplasms such as hepatocellular or prostate cancer. However, IMiDs are not always therapeutically active, because many patients develop resistance after initial clinical response, while some patients are resistant upfront. Given also the severe side effects accompanying and caused by the IMiD treatment, there is a need for a method for assessing the efficacy of an IMiD for use in therapeutic treatment before administration to a patient and for monitoring the efficacy of an IMiD over the course of the treatment. Therefore it was one object of the present invention to provide a method for assessing the efficacy of IMiDs in treatment of a malignant or premalignant disease or condition, such as hematological and non-hematological malignancies. There is also a need for the provision of an alternative treatment regimen to the IMiD treatment, wherein the subject to be treated has been identified as being resistant to IMiD treatment.
Despite the increasing clinical use, the molecular mechanisms that lead to the immunomodulatory, anti-angiogenic, anti-inflammatory and anti-proliferative effects of IMiDs have been unclear. Only recently, a direct molecular interactor of IMiDs named Cereblon (CRBN) has been identified. The expression of CRBN is essential for the effectiveness of IMiDs, and is crucial for both the teratotoxic as well as the anti-proliferative and immunomodulatory effects of IMiDs.
CRBN is described to be a DCAF (DDB1-CUL4-associated factor), which together with the scaffold protein CUL4, the Cullin adapter DDB1, and the E2 ligase binding RING domain protein ROC1 forms a functional E3 ubiquitin ligase complex of the CRL4 (Cullin4-Ring ligase) family. DCAFs act as the substrate-specific part of the CRL4 E3 ligases, which ubiquitinate various substrate proteins. The specific binding of substrates leads to the ubiquitination by CRL4cRBN ligase. Depending on the number of linked ubiquitin molecules and type of linkage there are mono-, multiple mono- or polyubiquitinations via lysine K6, K11, K27, K29, K33, K48 or K63, which each have different effects on the fate of the substrate. While K48 and K11-linked polyubiquitinations typically lead to proteasomal degradation, the remaining ubiquitinations rather determine non proteolytical fates of a protein (e.g. binding to other proteins or subcellular localization and protein trafficking). However, there are also E3 ligase components for which non-ligase functions have been described.
CRBN has been identified as a molecular interactor of IMiDs, but the cellular function of CRBN remains largely unclear. Notably, the two B-cell specific transcription factors IZKF1 and IZKF3 have recently been identified as substrates of CRBN, which are only targeted for proteasomal degradation upon treatment with IMiDs. While some immunomodulatory effects of IMiDs like modified IL2 secretion may be explained by the degradation of IZKF1 and IZKF3, the anti-proliferative, anti-angiogenic but also teratotoxic effects remain functionally unclear. Given the B-cell specific expression of IZKF1 and IZKF3, the efficacy of IMiDs in other malignancies like MDS cannot be explained. Moreover, no clear correlation between the expression or degradation of IZKF1 and IZKF3 due to IMiD treatment and the efficacy of the IMiD sensitivity of the cell lines was evident, thus limiting their application as predictive markers [1, 2].
Therefore, questions about the precise molecular mechanism of action of IMiDs, about parameters that predict therapeutic response, or about alternative therapeutic target structures were still unanswered. Although in several studies it has been tried to find a correlation of CRBN expression with the response to IMiD therapy, particularly in the therapy of multiple myeloma, the results were not conclusive. One study showed a correlation between CRBN expression at the protein level with the IMiD sensitivity of myeloma cell lines [3], while other studies have failed to demonstrate this relationship [4, 5]. Similar inconclusive results were shown when assessing CRBN mRNA levels in patient samples [6-8]. These contradictory results could be due, at least in part, to a lack of correlation between mRNA and protein expression levels as well as to a variety of different splice variants of CRBN which complicate a standardized diagnostic.
In summary it can be stated that the CRBN expression level (protein and/or mRNA) could be a potential predictive marker for the efficacy of IMiDs. This has, however, to be further examined due to the high complexity of the not yet understood molecular mechanisms involved. For example, as some myeloma cell lines are IMiD resistant despite exhibiting a high expression of wild-type CRBN, it is contemplated that other factors besides the CRBN expression alone could be responsible for the efficacy of IMiD treatment regimens.